I have a file named home.php that contains my home page (totally different to the rest of the site). As expected it loads correctly.
The problem is that it takes ages to load because it first searches through all my posts. I have narrowed down the problem and found that it is because in Settings->Reading it is specified as latest blog posts. The database call therefore occurs but none of the data is used. This would be ok apart from my site has hundreds of thousands of posts.
I can't specify the page as static as it isn't technically a wordpress page.